Abstract: Current reservoir interface prediction method of pre-drilling geosteering models works well in prediction of stabile formations,but it gives a relatively big error when predicting reservoir interfaces in a complex structural setting.Selecting appropriate adjacent wells and establishing a rectangular coordinate system with north direction as the y axis we calculated the horizontal displacement of the horizontal wells and the corresponding depth of the reservoir interface in the rectangular coordinate system,and built a 2D reservoir interface prediction model by using the mathematical method of curve fitting.This model is a binary function of horizontal displacement and reservoir interface.The reservoir interface prediction model is used to determine reservoir dips and calculate apparent dip angles and the relative displacement between bit and reservoir boundaries.The model is applied to predict a horizontal well in JL block,and the results show that the final reservoir interface prediction model is a quadratic function with a fitting degree of 68%.The predicted vertical depth of reservoir interface basically coincides with the actual vertical depth,and the predicted relief of reservoir interface is consistent with the actual relief on map view.The results show that the reservoir interface prediction model with a fitting degree of 68% built based on the data of 6 adjacent wells can meet the needs of landing and geosteering.The accuracy of the prediction results is positively correlated with the number of adjacent wells chosen.The results can provide guidance for geosteering of horizontal well and effectively keep the horizontal well within the target interval.

Key words: curve fitting, geosteering, horizontal well, reservoir interface, prediction